An off-duty California Highway Patrol officer spotted Gomes on fire, running, then collapsing, San Diego Police homicide lieutenant Todd Griffin said on Tuesday. Firefighters and police responded to his calls, but Gomes was pronounced dead at the scene, the Fox 5 San Diego TV station reported.

A preliminary investigation into the death showed that the death was “not a homicide but rather an accidental death or suicide,” Griffin added. Police are still investigating the cause of the fire, The New York Times reported.

Pyongyang then accused the American, who was 30 at the time, of illegally crossing its border with China.

They also said he had committed an unspecified “hostile act,” and in April 2010 sentenced him to eight years of hard labour and a fine of about $US700,000 (£456,000 at the time).

He remained detained for nine months until former President Jimmy Carter flew to North Korea and negotiated his release in late August that year, the Times said.

It’s unclear what Gomes, then an English teacher in South Korea, was doing in the North. His uncle, Michael Farrow, told CNN at the time that Gomes “may have just been trying to peek in and help others and teach them.”

An Associated Press file photo from January 2010, however, showed him at a human rights protest at the Imjingak Pavilion, near the Panmunjom demilitarised zone separating the two Koreas.

According to Gomes’s book, he endured “psychological torment of interrogation and confinement” under detention.

He also tried to commit suicide during that time, which included slitting his wrists and trying to starve himself, according to the San Diego Tribune, which cited Gomes’s mother, Jacqueline McCarthy.

After returning home, McCarthy said Gomes suffered from post-traumatic stress disorder, and began “isolating from the family,” opting to communicate via text than in person.

The most recent high-profile case of an American detained in North Korea was that of Otto Warmbier, who was sentenced to 15 years’ imprisonment last year after being accused of trying to steal a poster from his hotel. The 22-year-old was released back to the US this June while in a coma, and died six days after returning home.